There have been a variety of attempts to improve the wiping action of a windshield wiper to clean the outer surface of a windshield in cold weather. U.S. Pat. No. 3,718,940 shows an electric resistance heating element consisting of flat plate sections joined by coupling sections. The element is several thousandths of an inch in thickness and 1/8" (0.125") or more in depth. The element is within the wiper blade and is said to reinforce and thereby stiffen the blade. This limits the flexibility of the blade and inhibits its wiping action.
U.S. Pat. No. 3,936,901 discloses a blade having an internal cavity for receiving water and electrical heating elements. The elements and water distribute heat through the blade. The heating of water or ice, which then heats the blade, is an indirect and, therefore, ineffective means of heating the blade.
U.S. Pat. No. 4,152,808 discloses a heating element 1/8" (0.125") wide and 0.005" thick embedded in the sides of a frame adapted to receive a wiper blade. In the upward direction, heat is transferred to the frame and linkage elements. In the downward direction, heat is transferred from the element to the frame, from the frame through a gap in the wiper body carrying the blade and finally down to the blade. In the outward lateral direction, heat is transferreed to the surrounding air and essentially wasted. This indirect heating method is accordingly ineffective, inefficient, and limits the flexibility of the blade, thereby inhibiting the blade wiping action.
These most recent examples of the art contain electric heating elements which impede the flexibility of the wiper blade. The methods are indirect, ineffective and inefficient attempts to restore proper flexing and wiping action in cold weather. Proper flexing is particularly important given the substantial bending and compound curvature of current automobile windows.
In another approach, the windshield wiper frame and flexible linkages are enclosed in a heated envelope (U.S. Pat. Nos. 3,523,626 and 3,619,556). In U.S. Pat. No. 3,523,626, the envelope is filled with a heated fluid. These designs are meant to heat the frame and linkages to remove ice and snow which interfere with the movement of the frame and linkages. These heated envelopes are cumbersome and impede flexing action. In these indirect heating methods, electrical energy is used ineffectively and inefficiently in an attempt to improve the wiping action.
In summary, the foregoing prior art has not solved the problem of providing satisfactory wiping performance in frigid snowy and icy conditions while simultaneously removing and keeping the wiper blade, frame and linkages free from interference by ice and snow.